I thought that to be genuinely supersonic all the airflow over the airframe had to be greater than the local speed of sound. This does not occur until an aircraft speed of around M1.4 and therefore the band M0.8 to M1.3 is regarded as transonic. This is a dim recollection from undergraduate aerodynamics and I am open to correction.
I recently looked up some old Farnborough airshow clips on britishpathe. Aircraft top speed really did seem to be a huge selling point in those days. For example the Buccaneer is referred to as a "slowcoach" compared to the Phantom. Whilst this is correct in a game of Top Trumps the operational difference is not so clear-cut. It makes you wonder if some of the poor procurement decisions were made on the basis of headline performance figures that are all but irrelevant to the real world. Did their Airships regard M2.0 performance as a holy grail at the expense of range/payload in practical conditions?